This application is the National Phase of International Application No. PCT/DE01/00160, filed in Germany on Jan. 16, 2001 designating the United States of America, which claims priority to EP Patent Application No. 001 00 890.3, filed on Jan. 18, 2000.
The invention""s main scope of application is in movie projection, especially with 35 mm film.
The invention relates to a luminous projection objective. Known objectives of this type (DE-OS3833946) have been designed for the requirements with projections, whereby the focus is mostly on the grade of reproduction quality. Over many years this has led to a variety of modified Double Gauss objectives (DEOS 3633032, U.S. Pat. No. 4,704,011), which most of all sought to further reduce aberrations. Among other things, one result of this development is that in an advantageous design development, the diaphragm is preferably located in the larger space between the hollow inner surfaces of meniscus-shaped lenses, which is characteristic for Double Gauss objectives. However, this location, though advantageous for the correction of aberrations, exhibits significant disadvantages with projections, as the entrance pupil""s resulting location on the lighting side is not adjusted in the best possible manner. Documents DE-OS 3029929 and DE-OS 3029916 point out the pupils"" locations and their significance in relation to condenser adjustment in projections. The locations of entrance pupils, however, are not the only deciding factor in their best possible adjustment to lighting. Rather, the influence of solid angles above the lit object area on a partial luminous flux must be considered. These typical luminous flux diffusion characteristics require the adjustment of all object parameters relevant to lighting: location of an entrance pupil, opening and angles "sgr"RBa, as well as "sgr"RBi, restricting bundles. If this is not the case, such as with thus far known technical solutions, losses in the projected images"" illumination intensity are the result.
The purpose of the invention is an objective, respectively a series of objectives, which on one hand guarantees the most effective use of luminous flux diffusion throughout an entire object area and on the other hand exhibits image quality, which is better or the same as the image quality of known technical solutions being used with technologically advantageous glasses.
In accordance with the invention, this goal is accomplished with an objective according to the characteristics in claim 1. An objective according to the invention is characterized in that it maintains all effectivity parameters for adjustment to condenser systems in comparison to the aforementioned systems (DE-OS 3833946). Specifically, this indicates among other things an increase in the opening relationship from 1:2.4 to 1:1.9 and a reduction in vignetting of 61% to 73% for the most outward field point. This considerable expansion of the opening, axially as well as extra-axially, was achieved while maintaining image quality, including all image aberrations, when compared to the aforementioned systems.
The projection objective""s design development according to the invention is already different from known solutions according to documents U.S. Pat. Nos. 2,701,982, 2,897,724 and 3,005,379 in that they are system examples with sealing devices. Also, reproduction quality is substantially worse with these objectives. Furthermore, neither the number of lenses nor the sequence of refractive power and lens shape match in the objectives of U.S. Pat. No. 2,701,982 and 2,897,724. Though the sequence of refractive power is identical to a system as per U.S. Pat. No. 3,005,379, the shape is not. Only the first and last lenses are the same as far as shape is concerned.
According to claim 1, an objective according to the invention satisfies the stated conditional equations, guaranteeing the most effective adjustment to the condenser systems. In order to illustrate the characteristics of this component of the invention, the luminous flux diffusion of the condenser systems employed in the projection of movies must be explained in further detail. Luminous flux diffusion means a partial luminous flux"" dependence on the solid angle for a small area element at object level. A solid angle""s zero axis runs through the field point in view and is parallel to the lighting system""s axis. The characteristics of spatial luminous flux diffusion following in direction of projection behind this small area element contain all the properties of a condenser system relevant to lumen technology. The luminous flux"" diffusion depends on the object area and exhibits diffusion at the lighting system""s axis, which is virtually radial in symmetry. With smaller solid angles in the direction of the axis, the luminous flux is zero due to constructive necessity, it increases at a steep rise up to its peak value, and then flatly decreases outwardly. This diffusion changes outward via the object area. Radial symmetry is thereby lost, and the maximum of luminous flux diffusion moves in the direction in which the entrance pupil""s center appears, when seen from the lit field point. In that part of the bundle of rays, mirrored at the solid angle""s axis and located toward the maximum of luminous flux diffusion, the luminous flux is reduced significantly. Its maximum value only amounts to a fraction in comparison to the other portion of the bundle. Energetic diffusion therefore becomes highly asymmetrical.
For example, if objective aperture u=14.7xc2x0 (equivalent to a diaphragm value of k=1.9 at a fictitious projection distance of infinite) in the reproduction of an object area""s border sections and is therefore well adjusted to the lighting aperture, but the location of the entrance pupil LEP is  less than 100 mm, the result will be that an essential portion of the exterior entrance pupil area, which is located opposite the viewed field point in relation to the optical axis, is not at all involved in the reproduction; and on the other hand essential parts of luminous flux diffusion in the exterior entrance pupil area, located on the same side as the viewed field point in relation to the optical axis, are clipped, even with only minor vignetting. Furthermore, an aperture of only u=11.8xc2x0 (equivalent to k=2.4) will lead to yet larger losses of light, as portions of the luminous flux maximum""s environment are clipped. This effect is even greater with increased vignetting.
However, if the location of the entrance pupil is LEP greater than 400 mm with an aperture of u=14.7xc2x0, significant parts of the luminous flux"" diffusion are clipped by exterior entrance pupil areas, located opposite the viewed field point in relation to the optical axis, and the luminous flux has negligible values in the exterior entrance pupil areas, located on the same side as the field point viewed in relation to the optical axis. One must further observe that an entrance pupil""s location of LEP greater than 400 mm results in larger lens diameters on the object""s side and impedes the correction of aberrations.
This is the case with the mentioned systems (DE-OS 3833946), which are already known.
All these significant disadvantages have been removed with an objective according to the invention. An aperture of u=14.7xc2x0 (k=1.9) captures the energetically essential part of a luminous flux on the axis. In field range, the location of entrance pupil LEP and angles "sgr"RBa and "sgr"RBi, restricting the bundles, ensures that the objective captures the luminous flux infiltrating each area element in the field in the best possible manner and that the luminous flux is therefore utilized for the projection image""s illumination intensity. At the same time it is thus prevented that areas of the pupil are infiltrated by energetically non-essential bundles of light, which do not reasonably play a significant role in the composition, but unnecessarily impede the balance of reproduction aberration compensation and result altogether in worse reproduction quality.
One essential performance increase in optical reproductions with technologically advantageous glasses could only be achieved with a modified sequence of positive and negative refraction power, while largely maintaining a Double Gauss structure favoring aberrations, whereby it was necessary to allow for an increase in the lenses"" individual aberrations.
To produce a focal distance series in steps, necessary for the adjustment of projection conditions, using the same types of glass for equivalent lenses poses a decisive technological advantage. Furthermore, only technologically advantageous, i.e. process and cost effective glasses are used.
One preferred application of a projection objective according to the invention is the use of the objective alone, i.e. without additional components. It is entirely usual within the context of the invention to combine separate optical components with the projection objective. These components may, for example, be objective attachments or objective supplements, especially attachments for focal length variation and anamorphic attachments for panorama wide screen projection. It is conceivable to integrate attachments mechanically.